Systems, Methods, and Devices for Providing Networked Access to Media Signals

ABSTRACT

A system for providing networked access to media signals, the system comprising at least one virtual media card configured to interface with at least one application that produces and/or consumes media signals, and/or at least one media interface configured to interface with at least one physical media card that produces and/or consumes media signals. The system may also comprise a network interface configured to enable the system to exchange media signals with other devices on a common network, and a reference clock configured to provide a common clock signal to the at least one virtual media card, the at least one media interface, and the common network. An advertisement and discovery module configured to identify when the at least one application is started and/or stopped and when the at least one media card is attached and/or detached from the system may also be provided. The advertisement and discovery module is configured to: (i) make I/O channels of the at least one media card available to the system and the common network, and (ii) make I/O channels of the at least one application available to the system and the common network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/317,791, filed Dec. 9, 2016, which is the National Phase applicationof International Application No. PCT/AU2015/000345, filed 10 Jun. 2015,which designates the United States and was published in English, andclaims the benefit of priority to U.S. Provisional Application No.62/010,195, filed 10 Jun. 2014. These applications, in their entirety,are incorporated herein by reference.

This application is related to U.S. application Ser. No. 12/662,994,filed on May 14, 2010, now U.S. Pat. No. 8,005,939; U.S. applicationSer. No. 12/451,420, filed on Mar. 26, 2010, now U.S. Pat. No.8,171,152; U.S. application Ser. No. 12/308,168, filed on May 29, 2009,now U.S. Pat. No. 7,978,696; and International Application No.PCT/AU2007/000668, filed on May 17, 2007. Each of these applications areherein incorporated by reference in their entirety.

FIELD OF THE DISCLOSURE

This disclosure is related to systems, methods, and devices forproviding networked access to media signals (e.g., audio, video,multimedia signals). More particularly, this disclosure is related tosystems, methods, and devices for providing direct networked access tomedia signals from sound cards, virtual sound cards, and/orapplications.

BACKGROUND

Media signals, such as audio and video signals, within a computer orsimilar equipment (e.g., a PC or MAC) have historically been difficultto share across a network. Conventionally, software applications madespecific classes of signals inside the computer available on thenetwork.

For example, a virtual sound card may be capable of transferring audioto/from applications across a network. Such a virtual soundcard presentsa sound card interface to software applications and can transfer audiochannels to/from the network thereby providing networked channeltransmission for audio applications. A virtual sound card is presentedto applications in which each audio channel available to the applicationis associated with a single audio channel in the network. Signals may berouted to and from anywhere in the network to the channels associatedwith the application audio channels. From the network, the availablechannels are virtual soundcard channels—applications and sound cards(e.g. USB hardware) are not visible on the network.

In another example, the Skype application transfers audio from soundcards across the network for the Skype application. Skype providesnetworked channel transmission for sound cards. In this example, theaudio is not available outside of the Skype application.

Aggregate drivers are an example of a workaround to the inability forcomputers to share media content across a network. With an aggregatedriver, sound cards may be combined and their audio rate matched into asingle, larger audio interface which can be opened by applications thatcan only open a single sound card. In this fashion, the audio I/O frommany sound cards can be used by a multi-channel audio applicationwithout needing to open more than one sound card.

These existing techniques and workarounds do not sufficiently addressthe inability of systems to take media files from a computer and sharethem across a network.

Accordingly, it is desirable to have systems, methods and devicescapable of taking audio signals from sound cards and/or applications andmaking them available via a networked routing system.

SUMMARY

In exemplary embodiments, it may be desirable to have systems, methodsand devices capable of taking audio signals from sound cards and/orapplications and making them available via a networked routing system.For example, in exemplary embodiments, computer sound card input andoutput channels and/or application audio input and output channels maybe directly available on a network.

In exemplary embodiments, the sound card may comprise built-in analogueor digital ports, HDMI audio channels, USB, Firewire or Thunderboltconnected audio devices which can be attached and detached, the “defaultsystem input,” the “default system output” (which may be a mix of audiofrom multiple applications using the default system output) and/orvirtual sound cards (e.g. DVS, SoundFlower, aggregate driver).

In exemplary embodiments, application audio I/O may include audio comingout of iTunes or Windows Media player, audio going into a recordingapplication like Audacity, audio passing in and out of an applicationlike Skype, and/or audio signals going in and out of a virtual soundcard which is used for a specific set (e.g., one or more) ofapplications.

Exemplary embodiments described herein may provide a system (or acorresponding method or device) for providing networked access to mediasignals, the system comprising: at least one virtual media cardconfigured to interface with at least one application that producesand/or consumes media signals; at least one media interface configuredto interface with at least one physical media card that produces and/orconsumes media signals; a network interface configured to enable thesystem to exchange media signals with other devices on a common network;a reference clock configured to provide a common clock signal to the atleast one virtual media card, the at least one media interface, and thecommon network; and an advertisement and discovery module configured toidentify when the at least one application is started and/or stopped andwhen the at least one media card is attached and/or detached from thesystem; wherein the advertisement and discovery module is configured to:(i) make I/O channels of the at least one media card available to thesystem and the common network, and (ii) make I/O channels of the atleast one application available to the system and the common network.

In exemplary embodiments the media signals may be audio signals.

In exemplary embodiments the virtual media card may be a virtual soundcard.

In exemplary embodiments the media interface may be an audio interface.

In exemplary embodiments the at least one physical media card may be asound card.

In exemplary embodiments the system may further comprise a media routerconfigured to receive routing requirements and route the media signalsfrom the at least one application and the at least one sound card thatproduces media signals to the at least one application and the at leastone sound card that consume media signals.

In exemplary embodiments the system may further comprise a userinterface for enabling a user to create the routing configurations foruse by the media router.

In exemplary embodiments the user interface can be used to enable theconnection of any combination of I/O channels.

In exemplary embodiments the at least one media interface includes arate/phase matcher configured to match the rate and/or align the phaseof the media signals passing between the at least one media card and thesystem.

In exemplary embodiments the rate/phase matcher may use an asynchronoussample rate converter to align the media signals.

In exemplary embodiments the system may further comprise a mediatransceiver configured to control the rate at which medial signals areproduced and consumed by the at least one application, the at least onemedia card, and the other devices on the common network.

In exemplary embodiments the system may further comprise media buffersconfigured to temporarily store media signals to compensate for timingvariations within the system and the common network.

In exemplary embodiments each I/O channel has a network name constructedfrom the combination of a channel name and a device name.

In exemplary embodiments the virtual media card may be configured to beused by one application.

In exemplary embodiments the virtual media card may be configured to beused by multiple applications.

In exemplary embodiments the virtual media card may support a fixedchannel mode of operation.

In exemplary embodiments the virtual media card may support anapplication multiplexing/demultiplexing mode of operation.

In exemplary embodiments the virtual media card may support a fixedchannel mode of operation and an application multiplexing/demultiplexingmode of operation.

In exemplary embodiments the media signals provided to a single virtualmedia card from the multiple applications may be mixed together.

In exemplary embodiments the media signals provided to a single virtualmedia card from the multiple applications may not be mixed together.

Exemplary embodiments described herein may provide a system (or acorresponding method or device) for providing networked access to mediasignals, the system comprising: at least one virtual media cardconfigured to interface with at least one application that producesand/or consumes media signals; a network interface configured to enablethe system to exchange media signals with other devices on a commonnetwork; a reference clock configured to provide a common clock signalto the at least one virtual media card and the common network; and anadvertisement and discovery module configured to identify when the atleast one application is started and/or stopped; wherein theadvertisement and discovery module is configured to make I/O channels ofthe at least one application available to the system and the commonnetwork.

In exemplary embodiments the system may further comprise at least onemedia interface configured to interface with at least one physical mediacard that produces and/or consumes media signals; wherein the referenceclock may be configured to provide the common clock signal to the atleast one media interface; wherein the advertisement and discoverymodule may be configured to identify when the at least one media card isattached and/or detached from the system; and wherein the advertisementand discovery module may be configured to make I/O channels of the atleast one media card available to the system and the common network.

In exemplary embodiments the media signals may be audio signals.

In exemplary embodiments the virtual media card may be a virtual soundcard.

In exemplary embodiments the media interface may be an audio interface.

In exemplary embodiments the at least one physical media card may be asound card.

In exemplary embodiments the system may further comprise a media routerconfigured to receive routing requirements and route the media signalsfrom the at least one application and/or the at least one sound cardthat produces media signals to the at least one application and/or theat least one sound card that consume media signals.

In exemplary embodiments the system may further comprise a userinterface for enabling a user to create the routing configurations foruse by the media router.

In exemplary embodiments the user interface can be used to enable theconnection of any combination of I/O channels.

In exemplary embodiments the at least one media interface includes arate/phase matcher configured to match the rate and/or align the phaseof the media signals passing between the at least one media card and thesystem.

In exemplary embodiments the rate/phase matcher may use an asynchronoussample rate converter to align the media signals.

In exemplary embodiments the system may further comprise a mediatransceiver configured to control the rate at which medial signals areproduced and consumed by the at least one application, the at least onemedia card, and/or the other devices on the common network.

In exemplary embodiments the system may further comprise media buffersconfigured to temporarily store media signals to compensate for timingvariations within the system and the common network.

In exemplary embodiments each I/O channel may have a network nameconstructed from the combination of a channel name and a device name.

In exemplary embodiments the virtual media card may be configured to beused by one application.

In exemplary embodiments the virtual media card may be configured to beused by multiple applications.

In exemplary embodiments the virtual media card may support a fixedchannel mode of operation.

In exemplary embodiments the virtual media card may support anapplication multiplexing/demultiplexing mode of operation.

In exemplary embodiments the virtual media card may support a fixedchannel mode of operation and an application multiplexing/demultiplexingmode of operation.

In exemplary embodiments the media signals provided to a single virtualmedia card from the multiple applications may be mixed together.

In exemplary embodiments the media signals provided to a single virtualmedia card from the multiple applications may not be mixed together.

Exemplary embodiments described herein may provide a system (or acorresponding method or device) for providing networked access to mediasignals, the system comprising: at least one media interface configuredto interface with at least one physical media card that produces and/orconsumes media signals; a network interface configured to enable thesystem to exchange media signals with other devices on a common network;a reference clock configured to provide the common clock signal to theat least one media interface and the common network; and anadvertisement and discovery module configured to identify when the atleast one media card is attached and/or detached from the system;wherein the advertisement and discovery module is configured to make I/Ochannels of the at least one media card available to the system and thecommon network.

In exemplary embodiments the system may further comprise at least onevirtual media card configured to interface with at least one applicationthat produces and/or consumes media signals; wherein the reference clockmay be configured to provide a common clock signal to the at least onevirtual media card; wherein the advertisement and discovery module maybe configured to identify when the at least one application is startedand/or stopped; and wherein the advertisement and discovery module maybe configured to make I/O channels of the at least one applicationavailable to the system and the common network.

In exemplary embodiments the media signals may be audio signals.

In exemplary embodiments the virtual media card may be a virtual soundcard.

In exemplary embodiments the media interface may be an audio interface.

In exemplary embodiments the at least one physical media card may be asound card.

In exemplary embodiments the system may further comprise a media routerconfigured to receive routing requirements and route the media signalsfrom the at least one application and/or the at least one sound cardthat produces media signals to the at least one application and/or theat least one sound card that consume media signals.

In exemplary embodiments the system may further comprise a userinterface for enabling a user to create the routing configurations foruse by the media router.

In exemplary embodiments the user interface can be used to enable theconnection of any combination of I/O channels.

In exemplary embodiments the at least one media interface includes arate/phase matcher configured to match the rate and/or align the phaseof the media signals passing between the at least one media card and thesystem.

In exemplary embodiments the rate/phase matcher may use an asynchronoussample rate converter to align the media signals.

In exemplary embodiments the system may further comprise a mediatransceiver configured to control the rate at which medial signals areproduced and consumed by the at least one application, the at least onemedia card, and/or the other devices on the common network.

In exemplary embodiments the system may further comprise media buffersconfigured to temporarily store media signals to compensate for timingvariations within the system and the common network.

In exemplary embodiments each I/O channel may have a network nameconstructed from the combination of a channel name and a device name.

In exemplary embodiments the virtual media card may be configured to beused by one application.

In exemplary embodiments the virtual media card may be configured to beused by multiple applications.

In exemplary embodiments the virtual media card may support a fixedchannel mode of operation.

In exemplary embodiments the virtual media card may support anapplication multiplexing/demultiplexing mode of operation.

In exemplary embodiments the virtual media card may support a fixedchannel mode of operation and an application multiplexing/demultiplexingmode of operation.

In exemplary embodiments the media signals provided to a single virtualmedia card from the multiple applications may be mixed together.

In exemplary embodiments the media signals provided to a single virtualmedia card from the multiple applications may not be mixed together.

Other aspects, features, and advantages will become apparent from thefollowing description when taken in conjunction with the accompanyingdrawings, which are a part of the disclosure and which illustrate, byway of example, principles of the embodiments disclosed herein.

DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of thedisclosure as set forth herein, specific embodiments will now bedescribed by way of example and with reference to the accompanyingdrawings in which:

FIG. 1 is a network diagram of an exemplary embodiment of the systemsand methods described herein in the context of a networked environment;

FIG. 2 is a functional block diagram of an exemplary embodiment of thesystems and methods described herein;

FIG. 3 is an exemplary embodiment of a user interface for signal routingusing matrix mixing;

FIG. 4 is an exemplary embodiment of a user interface for signal routingwith mix groups;

FIG. 5A is an exemplary embodiment of a user interface for discovery androuting of media signal in which a USB device is disconnected;

FIG. 5B is an exemplary embodiment of a user interface for discovery androuting of media signal in which a USB device is connected;

FIG. 5C is an exemplary embodiment of a user interface for discovery androuting of media signal in which an application (e.g., iTunes) isdisconnected;

FIG. 5D is an exemplary embodiment of a user interface for discovery androuting of media signal in which an application (e.g., iTunes) isconnected; and

FIG. 6 is an exemplary embodiment of a user interface for internalrouting of networked channels.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

In exemplary embodiments, it may be desirable to have systems, methodsand devices capable of taking audio signals from sound cards and/orapplications and making them available to other components within anelectronic device and/or via a networked routing system. For example, inexemplary embodiments, computer sound card input and output channelsand/or application audio input and output channels may be directlyavailable to other components within an electronic device and/or on anetwork.

In exemplary embodiments, the sound card may comprise built-in analogueor digital ports, HDMI audio channels, USB, Firewire or Thunderboltconnected audio devices which can be attached and detached, the “defaultsystem input,” the “default system output” (which may be a mix of audiofrom multiple applications using the default system output) and/orvirtual sound cards (e.g., DVS, SoundFlower, aggregate driver).

In exemplary embodiments, application audio I/O may include audio comingout of a playback application like iTunes or Windows Media player, audiogoing into a recording application like Audacity, audio passing in andout of an application like Skype, and/or audio signals going in and outof a virtual sound card which is used for a specific set (e.g., one ormore) of applications. In embodiments, grouping a set of applicationsmay be necessary or desirable when it is difficult to e.g., separateper-application audio from a shared sound card.

In exemplary embodiments, the systems, methods and devices describedherein may be capable of providing direct networked access toinside-the-computer media (e.g., audio) signals. In particular, audiosignals from sound cards and/or applications may be advertised on thenetwork as network sources and sinks and may be discovered and patchedin the same way as other networked audio channels.

Applications may be started and stopped and sound card may beattached/detached from a computer or started/stopped in the case ofvirtual sound cards. For example, when a sound card is attached orstarted, the channels associated with it may be advertised on thenetwork. When a sound card is detached, the advertisements associatedwith the sound card channels may be removed. Similarly, when anapplication is started, the advertisements associated with theapplications' audio inputs and outputs may be created and when theapplication is stopped, the advertisements associated with theapplications' audio inputs and outputs may be removed.

In certain embodiments, it may be undesirable to have audio channels forsound cards and applications automatically appear on the network.Accordingly, in certain embodiments, a variety of policies may beapplied to limit what is automatically made available. For example,resources could be advertised unless they are on a “do not advertise”list. Alternatively, only resources on an explicit list of “allowedadvertisements” could be advertised. Advertised resources in this casemay be sound card channels, application audio inputs and outputs, or acombination of both. Other advertisement policies may also be supported.

As discussed herein, combining signals from several sound cards oftenrequires the use of software applications like aggregate drivers andexchanging audio between applications often requires some kind ofvirtual sound card interface. Aggregate drivers, inter-application audiosharing and networked virtual sound cards may be combined to exchangeaudio between applications, sound cards and the network but differencesin signal routing has distinguished inside-the-computer routing andvia-the-network routing.

When standalone applications are used (e.g., a combination of MacOSXAggregate Driver, SoundFlower and Dante Virtual Soundcard), signalrouting is managed by each separate software component with separateGUI/configuration settings. An application may be used to combineaggregate driver functionality (including routing between sound cards)and inter-application sharing but would still treat the networkinterface as a networked virtual sound card with a fixed number ofchannels. In such applications, audio signals may be routed aroundinside-the-computer including to/from the sound card side of thenetworked virtual soundcard and then signals may be routed to/fromchannels on the network side for the networked virtual sound card viathe network.

In contrast, the systems, methods and devices described herein integratethe functionality of aggregate drivers, inter-application audio sharingsystems and networked audio routing into a single, coherent signalrouting system. The inside-the-computer audio signal is available on thenetwork and has a unique network name. In exemplary embodiments, thenetwork name may be constructed from a channel label and a device name(e.g., BuiltIn-Left@laptop analogue audio input, oriTunes-Right@laptop). In exemplary embodiments, these signal names maybe used to express signal routing without distinguishing betweeninside-the-computer routing and across-the-network routing.Inside-the-computer and across-the-network may be configured in the sameway—using channel labels and device names (channel-label@device-name).Exemplary inputs to the routing system may include sound card input(e.g. USB analogue input, Soundflower), any networked channel source(e.g. Dante transmit channels), application audio outputs (e.g. Skype,iTunes audio), and/or a mixed audio output (e.g. the “Default SoundcardOutput” for an OS). Exemplary outputs from the routing system mayinclude sound card output (e.g. USB analogue output, Soundflower),networked channel receivers (e.g. Dante receive channels), Applicationaudio inputs (e.g. Skype, Audacity), and/or a default soundcard inputfor the OS.

In exemplary embodiments, signal names (e.g., channel-label@device-name)may be used in the routing system to express connections/patches for oneor more of the following:

-   -   Between inside-the-device audio signals and network channels.        Inside-the-device resources like hardware audio I/O ports and        application audio channels are now directly routable across the        network.    -   Between applications inside a single device    -   Between sound card I/O ports inside a single device        In exemplary embodiments, any combination of the types of        connections described may be allowed. In exemplary embodiments,        multiple output patches for any given signal may be supported,        implying that any signal can be replicated to more than one        output via the routing system. For example, a patch may be to        route USB-analogue-in@deviceA to Skype-Input@deviceB via the        network, since deviceA and deviceB are different devices. Or the        patch may be to route DAW-application-stereo-mix@laptop to        builtin-output@laptop, and DAW-application-stereo-mix@laptop to        stereo-input@mixing-console (i.e., the        DAW-application-stereo-mix signal may be replicated and passed        to a local sound card and across the network). Other exemplary        patches may include routing DefaultSystemOutput@laptop to        speaker@conference-room or routing        microphone@conference-room->SkypeInput@laptop.

In exemplary embodiments, the systems, methods, and devices describedherein may also utilize a reference clock to time align and rate matchthe media signals from the sound cards and applications. Typically,transmitters of signals over a network emit packets at a rate governedby an underlying hardware media clock (e.g., a sound card crystal). Withtypical computer equipment, audio sourced from each sound card attachedto the computer may be be transmitted at a slightly different rate dueto manufacturing variation in the media clock hardware (e.g., frequencyvariation of quartz crystals). Accordingly, a device receiving streamsfrom one or more sound cards must typically rate match and time alignthe incoming audio to the receiving sound card(s), which in turn may berunning at slightly different rates due to manufacturing variation.Specialized devices may support locking of the hardware media clock to areference clock (e.g., the Dante-MY16-AUD card and similar devices, orprofessional sound cards with word clock inputs), however typical soundcard hardware rarely supports an adjustable media clock. Typicalcomputer equipment receiving audio from two or more sound cards, eitherlocally attached or via a network stream, must rate match (andoptionally time align) incoming audio to the media clocks of thereceiving sound card(s) in order to ensure glitch free playout.

In exemplary embodiments, the systems, methods and devices describedherein may rate match and time align incoming audio to a sharedreference clock. For example, if the computer performing the method isattached to a network, the reference clock may be distributed via thenetwork and may be available to some or all media transmitters andreceivers. If the computer is not attached to a network, the referenceclock may be locally generated (conceptually the computer provides areference clock to a network of one device (itself)). In exemplaryembodiments, when the systems, methods and devices described herein aretransmitting and receiving streams of packets (e.g., using Dante, AES67,the AVB protocol suite, RTP, or some other networked media transportsystem) the shared reference clock used may be that which is provided bythe networked transport system. For example some standardized protocolsprovide a shared reference clock. The IEEE 1588 Precision Time Protocolversions 1 and 2 are commonly used with Dante, AES67 and RTP. The802.1AS Standard for Local and Metropolitan Area Networks—Timing andSynchronization for Time-Sensitive Applications in Bridged Local AreaNetworks may be used with the Audio Video Bridging (AVB) protocol suite.A stream of media packets (e.g. RTP or IEEE 1722) and the Network TimeProtocol (NTP) are also examples of shared reference clocks.

Although time alignment of signal capture and playout to a sharedreference clock is desirable for many applications, it is not requiredfor glitch-free capture and playout of audio in exemplary embodiments.For example, a system may use a reference clock that supports timealignment (e.g., IEEE 1588) merely to rate match outgoing audio, withoutensuring that the captured audio signals are time aligned to thereference clock. Likewise, playout of incoming audio may be rate matchedbut not time aligned.

In exemplary embodiments, a single device may be conceptualized as anetwork of one device. Audio signals within a single device may be ratematched and time aligned to a reference signal generated internally tothe device.

In exemplary embodiments, a shared reference clock used for ratematching may have one or more benefits. First, audio exchange betweensound cards, between network channels, and between sound cards andnetwork channels may be simplified since the rate difference between thesound card and the shared reference clock may be the only parameterwhich must be obtained. In other systems, a rate difference betweenevery received stream and each corresponding sound card was required,since each stream could be transmitted at the rate of source sound cardproducing the samples.

Second, the rate difference between each sound card and the sharedreference clock may be calculated without transmitting or receiving anymedia packets. In other devices, a rate difference between the incomingpacket stream and a local sound card was measured but since this ratedifference cannot be known accurately until several packets have beenreceived, additional buffering was required to ensure glitch freeplayout while an accurate rate difference estimate was acquired. Theadditional buffering may introduce extra latency. Additionally, sincepacket arrival jitter negatively affects rate estimation, many packetsmay be required to obtain a reasonably accurate estimate of the ratedifference between the incoming packet stream and the local sound cards.In contrast, the rate difference between a shared reference clock andthe local sound cards calculated by exemplary systems described hereinmay be continuously and frequently updated without requiring mediapackets, thereby enabling lower latency by eliminating unnecessarybuffering and reducing startup time.

Third, audio processing (e.g., mixing of signals) may be simplifiedsince the signals inside a device and on the network are rate matched toa common reference clock.

In exemplary embodiments, a shared reference clock supporting timealignment may have one or more of the following benefits (in addition tothose provided by rate matching alone).

First, the phase alignment of signals captured by different sound cardscan be preserved, even though each sound card may have a different mediaclock rate due to manufacturing variation. In exemplary embodiments, thephase alignment of captured signals may be preserved even between soundcards connected to different computers.

Second, the phase alignment of signals played out from different soundcards can be preserved, even though each sound card may have a differentmedia clock rate due to manufacturing variation. In exemplaryembodiments, signal playout phase alignment may be preserved evenbetween sound cards connected to different computers.

Third, compensation for fixed input and output delays in sound cards maybe applied, ensuring that signals passed through sound cards withdifferent delays remain time aligned.

Forth, time alignment information (i.e., rate difference and phaseoffset between the sound card and the shared reference clock) can becalculated without transmitting or receiving any media packets.Generally, time alignment between media streams has been achieved byincluding timestamps in media packets, for example RTP uses wall clocktimestamps to provide lip sync between a video stream and any associatedaudio streams. If the streams to be time aligned are sourced from thesame device, good alignment can be achieved since both streams containtimestamps obtained by a reference clock shared by bothstreams—typically the system time of day in the sending device. However,streams from different devices are typically not time aligned since manysystems do not have a shared reference clock and if they did, timealignment information may need to be computed for each incoming stream,which is complicated. In exemplary embodiments described herein, thetime alignment information (rate difference and phase offset between theeach sound card and the shared reference clock) can be continuously andfrequently updated without requiring media packets, supporting timealignment between the media streams regardless of source.

Fifth, virtual sound cards attached to exemplary systems, methods anddevices described herein (e.g., SoundFlower) and applications connectedto the exemplary systems, methods, and devices via a virtual sound cardinterface may be capable of sending and receiving time aligned audio.Accordingly, phase alignment of incoming signals and playback of outputsignals can be assured whether the signals are coming from one or morelocal sound cards or from other sources in the network. As a result,software applications can perform sophisticated signal processingoperations like beam steering or spatial location of audio sources sincephase alignment is preserved.

In exemplary embodiments, the systems and/or methods described hereinmay be implemented in software which may be executed in a computer. Inexemplary embodiments, the software may be responsible for transferringaudio signals between sound cards, applications and streams of networkpackets. FIG. 1 is a network diagram of an exemplary embodiment of thesystems and methods described herein in the context of a networkedenvironment. In particular, FIG. 1 shows the relationships between anexemplary embodiment of the software and its environment.

As shown in FIG. 1, the system may comprise one or more audio interfaces(Audio I/F). The Audio I/F may be the software layer used between audioapplications and sound cards. The Audio I/F may be provided by anoperating system (e.g., CoreAudio provided by Mac OS X).

FIG. 1 also comprises Virtual sound cards (VSC1-VSCN). In exemplaryembodiments, the software may define one or more such virtual soundcards. A virtual sound card is a sound card implemented in software. Inexemplary embodiments, to applications, virtual and hardware sound cardsmay be indistinguishable. In exemplary embodiments, the system mayprovide multiple virtual sound cards. For example, VSCN shown in thediagram is being used by several applications while VSC1 and VSC2 shownin the diagram each used by a single application only.

During normal operation, an audio channel provided by an applicationattached to a sound card is mixed together with the corresponding audiochannel from every other application and delivered to the Audio I/Fsoftware; and each audio channel provided by the Audio I/F toapplications is replicated to every corresponding application inputchannel. Exemplary systems and methods described herein, however, mayimplement audio interfacing components to enable audio passing to andfrom each application to be kept separate even though many applicationsare using the same virtual sound card interface (e.g., VSCN). Inexemplary embodiments, this may enable audio routing to specificapplications even when they share a virtual sound card interface, whichmay be important since sound card input and/or output cannot beconfigured in many applications (e.g., Microsoft PowerPoint) and manysuch applications will use the “system default” audio sound card inputand output settings.

The system may also include a network interface. The network interfacemay be used to advertise and discover available networked audiochannels, to exchange media packet streams with other devices on thenetwork and/or to configure signal routing in the system. Signal routingmay also be configured locally via e.g., a graphical user interface(GUI) application, configuration file, internal configuration messagesor similar mechanisms. Other devices attached to the network maycomprise the software as well, but they may also be using a generalmedia transport system like Dante, AES67, the AVB protocol suite or RTP.The network interface may also used be to distribute a reference clockthrough the network or receive a reference clock from the network.

In exemplary embodiments, the computer executing the software mayinclude one or more sound cards. The sound cards may be built-in to thecomputer or they may be external to the computer. Many types of externalsound cards (e.g., USB, Firewire and Thunderbolt) may be attached anddetached from the computer with or without warning. Accordingly, inexemplary embodiments, the resources provided by detachable sound cards(e.g., audio channels and their associated labels) may dynamicallyappear and disappear depending on device attachment.

In exemplary embodiments, the system may also support a StandaloneVirtual Sound Card (SVSC). There are several types of virtualsoundcards, notably aggregate drivers (which combine channels from twoor more sound cards into a single sound card) and inter-applicationsharing drivers (which typically copy audio from input channels tooutput channels in a loopback fashion). In exemplary embodiments, thesystems and methods described herein can be attached to standalonevirtual sound cards like the Mac OS X Aggregate Driver and SoundFlowervia standard audio interface APIs.

FIG. 2 is a functional block diagram of an exemplary embodiment of thesystems and methods described herein. In particular, FIG. 2 illustratesthe functional elements of an exemplary software implementation of thesystems and methods described herein. The elements inside the outermostbox are part of the exemplary system. Applications, sound cards, soundcard interfaces and the network interface that are outside the outermostbox and external to the system described herein but provided forcontext. In practice, an actual implementation of the systems andmethods described herein may combine the functional blocks or refactorthe blocks differently for reasons of efficiency, source codemanagement, performance, latency, etc.

As illustrated the system comprises a reference clock which provides aclock signal labelled as ref_clk in the diagram to many of the systemcomponents. In exemplary embodiments, the ref_clk signal may provide oneor both rate and phase/time alignment of information. The blocks labeled“VSC1”-“VSCN” (virtual sound card) in FIG. 2 show a ref_clk input sincethe reference clock may govern the rate at which audio samples aretransferred between the application and the virtual soundcard. Theblocks labeled “rate/phase match” in the diagram show a ref_clk inputsince an asynchronous sample rate converter can rate match andoptionally phase align audio passing between the audio buffers and theSound Cards 1-N. Appropriate control of the asynchronous sample rateconverter may require an estimate of the rate difference between eachsound card media clock rate and the reference clock and an estimate ofthe phase difference between each sound card media clock and thereference clock. The block labelled “media stream TX & RX” shows aref_clk input since the rate at which media packets are produced andconsumed may be directly governed by the ref_clk signal.

Additionally, media packets may be timestamped using the ref_clk signal,allowing the media contained in them to be time aligned at receivers.Typically, the system may be used in a network and may exchange audiowith other networked devices. In this case, the ref_clk signal may belocked to a shared network reference clock (e.g., provided by a networktime protocol like IEEE1588, 802.1AS or NTP, or provided by some otherstream of packets containing timing information). Alternatively, thesystem may provide a shared network reference clock by using a networktime protocol (e.g., IEEE1588, 802.1AS or NTP) to distribute the ref_clksignal throughout the network. Additionally, media packets transmittedby the system may contain timestamps derived from ref_clk and maytherefore be used by a device receiving a media stream from the systemto derive a clock which is slaved to the system ref_clk signal. Inexemplary embodiments, media packet stream transmitted by the systemwill at minimum provide information about the rate of the ref_clksignal, since the ref elk signal directly governs that rate at whichmedia packets are transmitted.

In exemplary embodiments, the media interfaces to the system aim totransfer audio at regular and predictable intervals, however interfacesmay be subject to timing variation to some extent. Depending on theinterface, timing variation magnitude can range from microseconds tomilliseconds to several seconds. For example, media packets mayexperience jitter in delay as they pass through a network containingother traffic; applications experience scheduling jitter as operatingsystems multi-task; and the timing of audio transfers to/from soundcards beats with respect to ref_clk according to the rate differencebetween the sound card media clock and wanders as the sound cardhardware clock varies with temperature. Accordingly, in exemplaryembodiments, the system may comprise audio buffers. The audio buffers inthe system may be configured to compensate for timing variation in thetransfer of media signals through the system interfaces to sound cards,applications and the network. The audio buffers in the system may alsobe used to delay signals so that they can be time aligned. For example,two hardware sound cards may have differing input and/or output delays.Delays may be introduced to compensate for fixed phase offsets betweensignals by storing audio samples in the audio buffers.

In exemplary embodiments, the system may also comprise an audiorouting/signal routing block. The audio routing block may be configuredto transfer input audio data from channels provided by applications,sound cards and media streams to the audio buffers and transfer outputaudio data from the audio buffers to channels accepted by applications,sound cards and media streams. In exemplary embodiments, the audiorouting system may transfer audio data between input and output channelsvia the audio buffers in accordance with the signal routing required bya given application.

From a user point of view, audio signal routing may be configured usingchannel labels and device names. The routing control block may convertthe label based signal routing specified by the user into simpler audiochannel routing configurations which in turn may control how the audiorouting block transfers audio data between the audio buffers andapplications, sound cards and media streams.

To allow several input signals to be simultaneously routed to a singleoutput port, the audio routing block may provide matrix mixingfunctionality. In exemplary embodiments, matrix mixing may comprise theability to construct output signals that are weighted sums of the set ofinput signals routed to that output port. Additionally, in exemplaryembodiments, an input signal may be routed to many output portssimultaneously.

FIG. 3 is an exemplary embodiment of a user interface for signal routingusing matrix mixing. In FIG. 3, four input channels (iTunes Left, iTunesRight, M-Track Mic Left and M-Trace Mic Right) are all routed to asingle mono output channel labeled “Built-in Speakers Left”. In thisrouting configuration, the output channel is the mix (i.e., weightedsum) of the four input channels. In the simplest mixing case, theweights are all 1.0, but in general each channel may have a differentweight (gain/attenuation) in the mix.

Accordingly, in exemplary embodiments, the audio routing block mayperform any or all of the four different tasks. The audio routing blockmay transfer audio samples between sound cards & audio buffers, transferaudio samples between virtual sound card interfaces & audio buffers,transfer audio samples between network audio streams & audio buffers,and/or combine two or more signals destined for the same output portusing a weighted sum.

As discussed previously and shown in FIG. 2, the system may comprise oneor more rate/phase match blocks which use an asynchronous sample rateconverter (ASRC) to adapt audio transferred between a sound card and theaudio buffers, ensuring glitch free, time aligned audio capture andplayback. In operation, a block of B samples passed through anAsynchronous Sample Rate Converter results in R*B samples at the outputwhere 1/R is the ratio between the input and output sampling rates. Inexemplary embodiments, the ASRC may change the sampling interval whilepreserving the audio signal represented by the sample values.

In exemplary embodiments, the rate difference can be estimated becauseperiodic events are triggered in the sound card interface layer at arate which is directly related to the sound card media clock. Theseevents are typically related to audio sample buffer transfers from thesound card to system memory and can be timestamped with ref_clk. Theresulting sequence of timestamps can be used to estimate the ratedifference between the sound card media clock and the ref_clk, and toestimate the phase difference between the sound card media clock and theref_clk. In exemplary embodiments, the rate/phase match block may userate and phase difference estimates in a Phase Locked Loop (PLL) tocontrol the ASRC ratio parameter such that the rate of samples providedto and consumed by the sound card interface is matched (or at leastsubstantially matched) to the rate of samples consumed by and providedto the system audio buffers over the long term. In exemplaryembodiments, this may be desirable for glitch free audio. Additionally,the phase difference between the sound card media clock (represented bythe phase of first sample in the audio buffer transfer after it has beenpassed through the ASRC) and the ref_clk is reduced over the short termand minimized (or at least substantially minimized) over the long term.

Phase Locked Loop (PLL) techniques for causing one clock to trackanother are well understood in the art and should be well understood bya person of ordinary skill in the art. In exemplary embodiments, thesound card media clock, adapted by the ASRC, may be caused to track theref_clk by adjusting the ASRC ratio parameter.

The system in FIG. 2 also comprises a plurality of virtual sound cardinterfaces (VSC1-VSCN). The virtual sound cards are interfaces betweenthe system and the audio applications. The interfaces appear as soundcards to the applications, however they may be implemented in software.Applications transfer audio through the virtual sound cards, to and fromthe system using standard sound card APIs such as CoreAudio. The rate atwhich audio samples and/or buffers are transferred between theapplication and the virtual sound cards is determined by the ref_clkinput to the VSC blocks.

In exemplary embodiments, the virtual sound cards may support two modesof operation (1) fixed channel (shown in FIG. 2 as blocks labeled VSC1and VSC2) and/or (2) application Mux/DeMux (shown in FIG. 2 as the blocklabeled VSCN).

In fixed channel mode of operation, the virtual sound card has a fixednumber of input and output channels. The virtual sound card providesinput and output channels to audio applications using a standard soundcard API (e.g. CoreAudio) and there is a one to one correspondencebetween audio channel buffers and virtual sound card inputs and outputs.Applications use a standard sound card API to transfer audio datato/from the virtual sound card, which in turn transfers audio datato/from the system audio buffers. In exemplary embodiments, typicalsound card behavior may apply in fixed channel mode. For example, audiooutput from applications sharing the same virtual sound card (e.g. App₂1-App₂K in FIG. 2) may be mixed together by the sound card API.Additionally, audio input provided to applications sharing the samevirtual sound card (e.g. App₂ 1-App₂K in FIG. 2) may be replicated foreach application connected to the virtual sound card by the sound cardAPI.

In the application Mux/Demux mode of operation, the virtual sound cardhas a fixed number of input and output channels, however additionalchannels are available between the audio routing block and the virtualsound card. The fixed input and output channels are labeled “Mix” inFIG. 2. The additional channels have a one-to-one association with audioapplications connected to the virtual sound card interface and arelabeled as App1, App2, . . . AppN in FIG. 2. Audio passing through theApp1 channel is exclusively sourced by App_(N) 1, or is exclusivelydestined for App_(N) 1. The audio passing through the App1 channel isnot mixed with audio from the other applications connected to VSCN(App_(N) 2-App_(N)K). Likewise, the audio passing through each set ofthe AppK channels is exclusively associated with application App_(N)K.Using such a system, audio may be routed to and from specificapplications even when they are attached to the same sound card.

In exemplary embodiments, the systems, methods and devices describedherein may also be capable of creating Mix groups. FIG. 4 is anexemplary embodiment of a user interface for signal routing using mixgroups. In exemplary embodiments, input channels may be mixed togetherby the audio routing block to form another set of channels called “MixGroups.” The new input and output channels created by a mix group may begiven labels and appear in the routing matrix in the same fashion as anyother channel in the system. This functionality may be desirable tocreate default input and default output mixes for applications connectedto virtual sound card interfaces as well as in many typical applicationswhere signals need be combined in flexible ways. In exemplaryembodiments, input and output channel labels associated with the mixgroup may appear in the routing matrix so that the input channels to bemixed together for each channel in the mix group may be selected; and/orchannels created by the mix group may be routed to soundcards,applications and across the network and even into additional mix groupinputs.

In exemplary embodiments, audio entering the system from an application,sound card or network stream may pass through one or more mix groupsbefore exiting the system as an audio channel to an application, soundcard or network stream.

As shown in FIG. 4, the matrix routing view includes two mix groupslabeled “From Apps” and “To Apps” respectively. In the embodiment shownin FIG. 4, the audio from the local microphone input labeled (“Built-InMic”) and a network microphone labeled (“Network Mic”) are mixed toprovide input channels for the recording application (“Rec App”). Theaudio from the “iTunes” application, a network source (“Net Source”) andthe microphone (“Built-In Mic”) are mixed together before beingtransmitted to a network connected loudspeaker (“Net Speaker”).

As described above, the fixed channels may behave like a typical soundcard—the audio output from applications sharing the same virtual soundcard is mixed together and audio input provided to applications sharingthe same virtual sound card maybe replicated for each applicationconnected via the sound card API. This behavior may be implemented bycreating a mix group for the fixed input channels and a mix group forthe fixed output channels when the virtual sound card is created. Themix group for the fixed input channels combines audio channels fromapplications according to user configuration. The mix group for thefixed output channels combines matrix input channels into audio channelssent to applications according to user configuration.

If an application has no specific route for its input channels, it mayreceive audio from the fixed channels labeled “Mix” in FIG. 2. If anapplication has no specific route for its output channels, audio itprovides may be mixed into the fixed channels labeled “Mix” in FIG. 2.

Alternatively, if an application has a specific route for its inputchannels, it may receive audio exclusively from the associated Appchannels (labeled App₁ . . . App_(N) in FIG. 2). Note that the matrixmixer provided by the audio routing block allows several input channelsto be mixed together into an output channel exclusively associated withan application. Conversely, if an application has a specific route forits output channels, it may transfer audio exclusively to the associatedApp channels (labeled App₁ . . . App_(N) in FIG. 2). Audio from thisapplication may not be mixed into the audio channels labeled “Mix”.

The audio resources (input and output channels) available to the systemfor routing may vary with time. In embodiments, every audio resource mayhave an associated label and device name (e.g.,channel-label@device-name). Signal routing between inputs and outputsmay be expressed in terms of channel labels and device names, regardlessof whether the signal is located inside the computer (e.g., sound cardsand applications) or somewhere on the network.

Audio resources may appear and disappear for a variety of reasons. Forexample, sound cards may be attached and/or detached to the system,applications may be started and/or stopped, network channels may appearand/or disappear as devices are added or remove from the network or asnetwork faults occur and are rectified, and mix groups are created ordeleted.

When audio resources appear, the system may associate each audio channelwith a channel label and device name (typically the name of the computerrunning the software) and advertises the availability of those channelson the network. The system may advertise audio channels as Dante networkchannels or any other advertisement systems may be used. The advertisedinformation may allow other devices connected to the network to discoverthe available channels and configure media packet streams to transferaudio to and from the audio resources inside the system.

When audio resources disappear, the system may remove the advertisementsassociated with the audio resources that are no longer available. OtherDante devices may be unable to discover the audio resources that are nolonger available and will therefore be unable to set up media streamsto/from the channels that are no longer available.

Dante Controller is an example of a standalone application that canperform signal routing through a network using the advertisementsprovided by the system described herein. In exemplary embodiments,signal routing may be a separate function from media signal transport.For example, Dante Controller may configure signal routing but doesn'tproduce nor consume media packet streams.

In exemplary embodiments, the advertise and discover block may sense thearrival and departure of available audio resources in a variety of ways,including, but not limited to: USB hot plug events as devices areattached and detached (Firewire and Thunderbolt have similar events);impedance sensing events detecting the presence or absence ofconnections to input or output ports; network interface events such aslink up and link down; appearance and disappearance of Dante channeladvertisements on the network; and/or information provided by the systemVirtual Sound Card (VSC) interfaces as applications start and stop,attaching to and detaching from the VSC interface; and notificationsfrom other functional blocks such as routing control and/or audiorouting that mix groups have been created or deleted, channel labelshave been changed, parameters have changed (e.g. sample rate or numberof channels), etc.

In exemplary embodiments, information about the arrival and departure ofaudio resources may be provided to other functional blocks inside thesystem to facilitate instantiation and reclamation of functional blocksas needed (e.g., rate/phase match blocks associated with removable soundcards); to support timely creation and removal of network channelresources and media packet streams; and to trigger the configuration ofsignal routing via the “Audio Routing” block.

The input and output channels of USB sound cards may be formed byconcatenating the device name provided by the USB sound card driver anda short identifier. If the device is a single channel, no shortidentifier need be appended. If the device has two channels, theidentifiers “Left” and “Right” may be appended (e.g., “M-Track Mic Left”and “M-Track Mic Right”). If the device has more than two channels, anumber 1 . . . N may be appended. If the USB sound card driver cansupply non-numeric channel labels, these may be appended instead ofdigits or the left/right labels. If several USB devices with the sameUSB device name are attached, a digit may be inserted into the channellabel after the device name to disambiguate the channel labels for eachdevice.

The input and output channels of Virtual Sound Cards running in fixedchannel mode may be advertised with names derived from the name providedto the virtual sound card interface. For example, if the virtual soundcard interface was called “DAW”, the advertised channels may be labeled“DAW In 1” “DAW In 2”, . . . “DAW In 16”, “DAW Out 1”, . . . “DAW Out16”).

The “Mix” channels of a virtual sound card interface running inapplication Mux/DeMux mode may be advertised with names derived from thename provided to the virtual sound card interface. For example, the“Mix” channel labels for a two input, two output virtual sound cardinterface with name “Default” may be “Default In Left”, “Default InRight”, “Default Out Left”, “Default Out Right”.

The “App” channels of a virtual sound card interface may be advertisedwith names derived from the application attached to the interface. Forexample, assuming the application is called Skype the channels may belabeled “Skype In” and “Skype Out”. Presets describing default channellabels for specific applications allow sensible labels to be applied toapplications.

It may be desirable that audio resources be assigned consistent labelseven when they are attached and detached from the system. It may bedesirable that the inputs and outputs of a USB sound card remain thesame as it is attached and detached. This may allow audio signals to berouted and configured with stable names. Additionally, it may bedesirable that two identical sound cards retain the labels associatedwith each of their inputs and outputs regardless of which order they areattached and detached. In exemplary embodiments, USB and Firewiredevices may have unique identifiers which may be used to restore thecorrect labels when a device is reattached to a system. The situationmay be more difficult with applications, since several copies of a givenapplication can be attached to a virtual sound card at the same time. Tothe extent that it is possible, in exemplary embodiments, a stablechannel label may be derived from a combination of the application nameand associated user name associated with each instance.

In general, the user may override channel labels for a given audioresource and those changes may or may not be persistent. In exemplaryembodiments, the system may be capable of storing the channel labelsconfigured by the user and (assuming the audio resources the labelrefers to can be unambiguously identified) the system may use the samelabels for the channels the next time the device is plugged in, or thenext time the application is started.

Channel labels within a Rialto device must be unique. Across thenetwork, channel labels are scoped by a device name and the device namemust in turn be unique throughout the network in order for achannel-label@device-name to uniquely identify an audio resource in thenetwork.

As illustrated, the system shown in FIG. 2 also comprises a media streamTX and RX block which may be responsible for sending and receiving audiosignals across the network. The system may use Dante network channels,however other signal transports could be used including, but not limitedto, AES67, the AVB protocol suite and/or RTP.

In response to configuration by the user, the routing control block mayinstruct the media stream TX & RX block to transmit or receive a mediapacket stream and/or transfer audio samples between the media packetstream and the system audio buffers. The rate at which media packets areproduced and consumed is directly governed by the ref_clk. The precisemapping of audio channels to media packet streams is a matter of policyand is decided by the routing control block.

The system in FIG. 2 also comprises a routing control block whichconfigures the various functional blocks inside the system to achievethe routing configuration expressed by the user in signal labels. When alabel based routing change is made, the Routing Control block may needto:

-   -   Discover network channels and their parameters.    -   Configure the media stream TX & RX block to send audio channels        to another networked device or receive channels from another        networked device in media packet streams.    -   Reconfigure audio channel transfer mapping to/from an existing        media packet stream to/from the system audio buffers.    -   Reconfigure audio routing block channel routing to match the        desired signal routing specified by the labels.    -   Alter the audio channel transfer mappings for the VSC interfaces        operating in Mux/DeMux mode, for example when a specific route        to an application is added or removed.    -   Reconfigure audio channel transfer mappings to/from audio        buffers associated with mix groups.

In exemplary embodiments, the routing control block listens to eventsgenerated by the advertise & discover block as audio resources appearand disappear, and carries out the actions required to restore audioroutes configured previously or removes routes that are no longerrequired. Example of events that may need such action include, withoutlimitation, a removable sound card is attached, a removable sound carddetached, an application connected to a VSC interface is started, anapplication connected to a VSC interface is stopped, a network channelbecomes available, a network channel disappears and/or a custom mixgroup is created or deleted.

In exemplary embodiments, in order to transmit and receive signalsacross the network, the routing control block may need to use theadvertise & discover block to acquire the information needed to createmedia packet streams, for example: IP addresses, port numbers, channelmappings, audio formats, sample rates, etc.

FIGS. 5A-5D are exemplary embodiments of a user interface for discoveryand routing of media signal. As illustrated, these figures illustrate acontroller matrix routing view as audio resources appear and disappearin a computer running the system described herein. The controller matrixview shows network channel inputs and outputs. In exemplary embodiments,signals may be routed between inputs and outputs by clicking on a crosspoint.

FIG. 5A is an exemplary embodiment of a user interface for discovery androuting of media signal in which a USB device is disconnected. When theUSB device is disconnected, the labels for its channels cannot beresolved. This is why there are two circular symbols shown next to theSpeakers input channels in the Dante Controller view.

FIG. 5B is an exemplary embodiment of a user interface for discovery androuting of media signal in which a USB device is connected. When the USBdevice (M-Track Mic) is connected, new Dante transmit channels arecreated for each USB microphone channel. The channel labels may beconstructed by concatenating the USB device name “M-Track Mic” and theUSB sound card driver labels for the channels (i.e. the words “Left” and“Right”).

FIG. 5C is an exemplary embodiment of a user interface for discovery androuting of media signal in which an application (e.g., iTunes) isdisconnected. When the iTunes application is not running, the labels forits channels cannot be resolved. This is why there are two circularsymbols shown next to the Speakers input channels in the DanteController view.

FIG. 5D is an exemplary embodiment of a user interface for discovery androuting of media signal in which an application (e.g., iTunes) isconnected. When an audio application (iTunes) is started, the channellabels for its outputs are constructed by concatenating the applicationname (iTunes) with the labels “Left” and “Right” which can be assumedbecause the virtual sound card only has two channels.

FIG. 6 is an exemplary embodiment of a user interface for internalrouting of networked channels which shows how the controller (whichconfigures routing between network channels) can be used to configureaudio routing inside a computer running a system such as the systemdescribed herein. In FIG. 6, the output from iTunes is routed to thedefault sound card output for the computer. The routing is entirelyinternal to the computer. No signals cross the network as media packetstreams.

While embodiments of the have been shown and described herein, it willbe obvious to those skilled in the art that such embodiments areprovided by way of example only. It is intended that the followingclaims define the scope of the invention and that methods and structureswithin the scope of these claims and their equivalents be coveredthereby.

1. A system for providing networked access to media signals, the systemcomprising: at least one virtual media card configured to interface withat least one application that produces and/or consumes media signals; atleast one media interface configured to interface with at least onephysical media card that produces and/or consumes media signals; anetwork interface configured to enable the system to exchange mediasignals with other devices on a common network; a reference clockconfigured to provide a common clock signal to the at least one virtualmedia card, the at least one media interface, and the common network;and an advertisement and discovery module configured to identify whenthe at least one application is started and/or stopped and when the atleast one media card is attached and/or detached from the system;wherein the advertisement and discovery module is configured to: (i)make I/O channels of the at least one media card available to the systemand the common network, and (ii) make I/O channels of the at least oneapplication available to the system and the common network.
 2. Thesystem of claim 1, wherein the media signals are audio signals.
 3. Thesystem of claim 1, wherein the virtual media card is a virtual soundcard.
 4. The system of claim 1, wherein the media interface is an audiointerface.
 5. The system of claim 1, wherein the at least one physicalmedia card is a sound card.
 6. The system of claim 1, further comprisinga media router configured to receive routing requirements and route themedia signals from the at least one application and the at least onesound card that produces media signals to the at least one applicationand the at least one sound card that consume media signals.
 7. Thesystem of claim 6, further comprising a user interface for enabling auser to create the routing configurations for use by the media router.8. The system of claim 7, wherein the user interface can be used toenable the connection of any combination of I/O channels.
 9. The systemof claim 1, wherein the at least one media interface includes arate/phase matcher configured to match the rate and/or align the phaseof the media signals passing between the at least one media card and thesystem.
 10. The system of claim 9, wherein the rate/phase matcher usesan asynchronous sample rate converter to align the media signals. 11.The system of claim 1, further comprising a media transceiver configuredto control the rate at which medial signals are produced and consumed bythe at least one application, the at least one media card, and the otherdevices on the common network.
 12. The system of claim 1, furtherercomprising media buffers configured to temporarily store media signalsto compensate for timing variations within the system and the commonnetwork.
 13. The system of claim 1, wherein each I/O channel has anetwork name constructed from the combination of a channel name and adevice name.
 14. The system of claim 1, wherein the virtual media cardis configured to be used by one application.
 15. The system of claim 1,wherein the virtual media card is configured to be used by multipleapplications.
 16. The system of claim 1, wherein the virtual media cardsupports at least one of: (i) a fixed channel mode of operation; (ii) anapplication multiplexing/demultiplexing mode of operation; and (iii) afixed channel mode of operation and an applicationmultiplexing/demultiplexing mode of operation.
 17. (canceled) 18.(canceled)
 19. The system of claim 1, wherein the media signals providedto a single virtual media card from the multiple applications are mixedtogether.
 20. The system of claim 1, wherein the media signals providedto a single virtual media card from the multiple applications are notmixed together.
 21. A system for providing networked access to mediasignals, the system comprising: at least one virtual media cardconfigured to interface with at least one application that producesand/or consumes media signals; a network interface configured to enablethe system to exchange media signals with other devices on a commonnetwork; a reference clock configured to provide a common clock signalto the at least one virtual media card and the common network; and anadvertisement and discovery module configured to identify when the atleast one application is started and/or stopped; wherein theadvertisement and discovery module is configured to make I/O channels ofthe at least one application available to the system and the commonnetwork. 22-41. (canceled)
 42. A system for providing networked accessto media signals, the system comprising: at least one media interfaceconfigured to interface with at least one physical media card thatproduces and/or consumes media signals; a network interface configuredto enable the system to exchange media signals with other devices on acommon network; a reference clock configured to provide the common clocksignal to the at least one media interface and the common network; andan advertisement and discovery module configured to identify when the atleast one media card is attached and/or detached from the system;wherein the advertisement and discovery module is configured to make I/Ochannels of the at least one media card available to the system and thecommon network. 43-62. (canceled)